Photosensitive elements are used in image-reproduction processes and are well-known in the graphic arts industry. These elements are usually exposed to actinic radiation through an image-bearing transparency, such as a color separation transparency, to produce an image which is either a positive or negative with respect to the transparency used. Positive-working photosensitive elements are described in Chu and Cohen, U.S. Pat. No. 3,649,268 and negative-working photosensitive elements are described in Chu and Fan, U.S. Pat. Nos. 4,174,216 and 4,191,572. Negative-working elements produce an image that is the reverse of the transparency through which they are exposed. That is, the colored regions of the transparency are uncolored in the imaged element and the uncolored regions in the transparency are colored in the imaged element. Positive-working elements produce an image which is a duplicate of the transparency through which they are exposed. That is, the colored regions of the transparency are also colored in the imaged element and the uncolored regions in the transparency are uncolored in the image element. After imagewise exposure, the photosensitive elements may be developed by (a) washout of soluble image areas, (b) peeling apart, (c) toning with a colorant, or (d) combinations of these techniques.
Photosensitive elements are widely used in off-press color proofing to simulate the images produced by printing. Off-press color proofs include overlay systems and surprint, or single sheet systems. In an overlay proof, each colored image is on a separate transparent support sheet. The individual films are assembled in register and viewed as a composite against an appropriate background, e.g., an opaque reflective white sheet. In an overlay system, the individual colored images remain separable and can be combined separately. In a surprint proof, all of the colored images are superposed by, for example, multiple exposure, lamination, or transfer, on a single support. The colored images can not be separated and viewed individually.
Many conventional proofing films are precolored by their manufacturers. Thus, in the preparation of images from precolored proofing films, the operator is limited to those colors provided by the manufacturer. In addition, the cost of manufacture and distribution allows only a limited range of colors to be available.
It has been found that greater color flexibility can be attained from tonable elements. The operator can mix the toners supplied by the manufacturer as desired, and thus, toned images with an almost unlimited variety of colors can be prepared. Instead of many specialty films, the manufacturer need only supply a single, non-colored, tonable element.
Following imagewise exposure, tonable photosensitive elements typically are developed by washing out the unexposed areas of the photosensitive layer with a suitable solvent. Many of these elements require washout with an organic solvent which is disadvantageous for environmental and safety reasons. For example, Fan, U.S. Pat. No. 4,053,313 discloses a photosensitive element comprising a solvent-processable photosensitive layer, a tonable elastomeric layer, and a support, that is washed-out by a mixture of water and organic solvent. Similarly, the elements disclosed in Speckler, U.S. Pat. Nos. 4,376,158 and 4,376,159, require aqueous base for washout. The use of organic solvents is frequently undesirable because of flammability, toxicity, and waste disposal considerations. The use of aqueous base is also undesirable because of toxicity, waste disposal, and corrosion problems. Thus, there continues to be a need for improved tonable, photosensitive elements that can be processed in aqueous solvents, preferably with ordinary tap water.